Number of groups on the central atom of CH4, H20, H3O+, NH3, NH4+, CCI3F, CO2, CO32+ ?

In the question, it should be CO₃²⁻ instead of CO₃²⁺.

In CH₄, there are 4 H atoms on the central C atom.

In H₂O, there are 2 H atoms on the central O atom.

In H₃O⁺, there are 3 H atoms on the central O atom.

In NH₃, there are 3 H atoms on the central N atom.

In NH₄⁺, there are 4 H atoms on the central N atom.

In CCl₃F, there are 4 atoms (3 Cl and 1 F) on the central C atom.

In CO₂, there are 2 O atoms on the central C atom.

In CO₃²⁻, there are 3 O atoms on the central C atom.